The epidemiology of psoriatic arthritis in Olmsted County, Minnesota, USA, 1982-1991.

To determine the incidence, prevalence, and outcomes of psoriatic arthritis (PsA) in a geographically defined community.Using the Rochester Epidemiology Project computerized medical record system, we screened all records of Olmsted County, Minnesota, residents with any diagnosis consistent with psoriasis and/or PsA made between January 1, 1982 and December 31, 1991. Medical records were reviewed using a pretested data collection form. Only those cases of psoriasis where the diagnosis was confirmed by a dermatologist were included. PsA was defined as inflammatory arthritis associated with a definite diagnosis of psoriasis. All identified cases were followed until death, migration from the county, or January 1, 1992. Cases with seropositive rheumatoid arthritis, systemic lupus erythematosus, crystal induced arthritis, Reiter's syndrome, arthritis associated with inflammatory bowel diseases, and inflammatory osteoarthritis were excluded. Clinical characteristics were described using summary statistics. Age and sex adjusted incidence and prevalence rates were calculated. Survival was estimated using the Kaplan-Meier method.We reviewed the records of 1844 patients with a diagnosis of psoriasis. In 1056 of these, the diagnosis was confirmed by a dermatologist. Among these 1056 psoriasis cases, we identified 66 cases (34 female, 32 male) of PsA first diagnosed between 1982 and 1991. The average age and sex adjusted incidence rate per 100,000 US population was 6.59 (95% confidence interval, CI, 4.99, 8.19) and the prevalence on January 1, 1992, was about one per 1000 (95% CI 0.81, 1.21). The average age at diagnosis was 40.7 years. At diagnosis, 91, 3, and 6% of cases had oligoarthritis, polyarthritis, and spondylitis, respectively. Over the 477.8 person-years of followup, 25 developed extraarticular manifestations (enthesitis, n = 15; ocular inflammation, n = 11; urethritis, n = 9), 10 patients received disease modifying antirheumatic drug treatment (methotrexate, n = 7; sulfasalazine, n = 5; intramuscular gold, n = 1; oral gold, n = 1), 3 received corticosteroids, and 5 had surgical interventions (synovectomy, n = 3; arthroplasty, n = 1; other reconstructive surgery, n = 2). Survival was not significantly different from the general population (p = 0.546).Unlike results from previous referral based studies, our findings indicate that PsA is a mild, uncommon inflammatory arthritis, not associated with a significant increase in mortality.